Surface-emitting laser elements (or vertical cavity surface-emitting laser elements—VCSELs) are characterized in that laser light can be emitted in a perpendicular direction to the principal surface of a substrate formed with the element and in that the element has low threshold current and high power conversion efficiency. In addition, surface-emitting laser elements have various advantages, for example, that they emit circular light whose cross-section perpendicular to the optical axis is circular, that two-dimensional arrangement of them is facilitated, and that on-wafer inspection of them can be carried out efficiently. A VCSEL is suitable for use as the light source in various consumer applications, for example, an image forming apparatus, an optical pickup device, the optical communication data transmitter of optical interconnections and optical modules, etc. Optical modules made with VCSELs also have applications in high-speed transmission of light. At least in part due to such advantages, it is expected that the demand for surface-emitting laser elements as light sources for high-speed data communications will increase in the future.
In using a surface-emitting laser element for a light source for data communications, it generally is desirable for the element to have a structure capable of operating at high speed. In order for the surface-emitting laser element to accomplish a high-speed operation 10-40 Gbit/s and above, for example, it is especially desirable to optimize or otherwise improve characteristics such as low beam divergence, narrow laser line width, low junction temperature, and/or the like. Thus, it is desirable to provide a semiconductor light-emitting element that reduces one or more of beam divergence, narrow laser line width, and low junction temperature.
Certain example embodiments, as described below, help address these and/or other aspects. According to one example embodiment, a surface-emitting laser comprises a top mirror and a bottom mirror, at least one oxide section formed between the top and bottom mirrors, a light emitting cavity region formed between the oxide section and the bottom mirror, and a phase matching section with a graded index layer made of semiconductor thin films such that the total length of the oxide section, the light emitting cavity region and the phase matching section is 1.75 times an emitting wavelength of the surface-emitting laser, and the distance from center of the quantum wells to the center of the oxide layer being 0.75 times the emitting wavelength. The top mirror and the bottom mirror are each made with multilayers of semiconductor thin films with alternative indices of refraction. The at least one oxide section is formed between the top and bottom mirrors and comprises a stacked plurality of layers of semiconductor thin film of which at least one semiconductor thin film layer is provided as an oxide layer having an aluminum content of at least 98%. The light emitting cavity region, has a plurality of quantum wells and a plurality of barrier layers formed from semiconductor thin film with the quantum wells including InxGaAs where x=0-1 and the barriers including either AlxGaAs barriers where x=0-0.4 or GaAs1-yPy where y=0.2-0.3.
Layers of the oxide section and the phase matching section may be adjusted such that the 1/e2 width of beam divergence value is between 15-26 degrees, and such that the spectral RMS line width value be less than 0.45 nm. A layer in the oxide section above the oxide layer may be a graded composition layer with high aluminum content above 98% and a thin layer in the oxide section below the oxide layer may include Al0.9GaAs, the oxide layer may include high aluminum content above 98% and may be p-doped at 2.5×1018 cm−3, and the bottom mirror may include alternating refractive index layers made from AlxGaAs where x=0.12 & 0.9-1 for 850 nm wavelength and with x=0 & 1 for 1060 nm wavelength.
An aperture in the oxide layer may be configured such that HEdge≤3×Htip, where HEdge is a height of the oxide layer at an edge furthest from the aperture, and Htip is a height of the oxide layer closest to the aperture.
The aperture may be configured such that WAlAs≤WAlOx, where the aperture provides an opening of length WAR, in the oxide layer, and the oxide layer extends for a length WAlOx on either side of the aperture.
A substrate of the surface-emitting laser may comprise n-doped, p-doped, or un-doped GaAs.
The substrate may be oriented 2 degrees-off axis along a selected plane.
In the layer above the at least one oxide layer in the oxide section, a linear grading may be used for the aluminum content Al(x), where x ranges from 1.0 to 0.15 from start to end of the layer.
The top mirror may be either linearly doped or modulation doped.
The top contact layer comprising p++ GaAs may be provided above and adjacent to the top mirror, and the top contact layer may be terminated either as in-phase or anti-phase and may include a surface relief structure to control photon lifetime for achieving higher bandwidths.
The top mirror may include three to four AlxGaAs layers with aluminum content at 96%.
The at least one oxide section may comprise a first oxide layer and a second oxide layer, both having aluminum content at 98% or greater, at an optical distance of 0.5λ from each other.
A first oxide layer and a second oxide layer may be located above and below, respectively, of the multiple quantum well gain region, and a graded spacer layer may be adjusted such that the optical cavity is at its shortest cavity length of 0.5λ.
Another example embodiment provides a method for forming a surface-emitting laser using an epitaxial process. The method includes providing a top mirror and a bottom mirror, providing at least one oxide section formed between the top and bottom mirrors, providing a light emitting cavity region formed between the oxide section and the bottom mirror, and providing a phase matching section with a graded index layer made of semiconductor thin films, such that a total length of the oxide section, the light emitting cavity region and the phase matching section is 1.75 times an emitting wavelength of the surface-emitting laser, and the distance from center of the quantum wells to the center of the oxide layer is 0.75 times the emitting wavelength.
The top mirror and the bottom mirror may each be made with multilayers of semiconductor thin films with alternative indices of refraction. The at least one oxide section, formed between the top and bottom mirrors, comprises a stacked plurality of layers of semiconductor thin film of which at least one semiconductor thin film layer is provided as an oxide layer having an aluminum content of at least 98%. The light emitting cavity region formed between the oxide section and the bottom mirror may have a plurality of quantum wells and a plurality of barrier layers formed from semiconductor thin film with the quantum wells including InxGaAs where x=0-1 and the barriers including either AlxGaAs barriers where x=0-0.4 or GaAs1-yPy where y=0.2-0.3. Layers of the oxide section and the phase matching section may be adjusted such that the 1/e2 width of beam divergence value is between 15-26 degrees, and such that the spectral RMS line width value be less than 0.45 nm. A layer in the oxide section above the oxide layer may be a graded composition layer with high aluminum content above 98% and a thin layer in the oxide section below the oxide layer may include Al0.9GaAs. The oxide layer include high aluminum content above 98% and is p-doped at 2.5×1018 cm−3. The bottom mirror includes alternating refractive index layers made from AlxGaAs where x=0.12 & 0.9-1 for 850 nm wavelength and with x=0 & 1 for 1060 nm wavelength.
Another example embodiment provides a surface-emitting laser comprising a top mirror and a bottom mirror, each comprising a stacked plurality of layers of semiconductor thin film having alternating indices of refraction; at least one oxide section, formed between the top and bottom mirrors, comprising a stacked plurality of layers of semiconductor thin film of which at least one semiconductor thin film layer is provided as an oxide layer having a high aluminum content; a light emitting cavity region, formed between the oxide section and the bottom mirror, having a plurality of quantum wells and a plurality of barrier layers formed from semiconductor thin film; and at least one phase matching section having a graded index layer of semiconductor thin film. The composition and a dimension of one or more of the oxide section, the light emitting cavity region, and the at least one phase matching section are determined such that a predetermined phase relationship for reducing an effective refractive index difference between core and clad of the surface emitting laser is satisfied among the oxide section, the light emitting cavity region, and the at least one phase matching section.
The total length from the top end of the oxide layer to the bottom end of the phase matching layer may be determined so as to correspond to a first value equal to an emitting wavelength multiplied by a first constant, and the total length of the light emitting region is determined so as to correspond to a second value equal to the emitting wavelength multiplied by a second constant. The first constant can be 1.75 and the second constant can be 1.0.
The distance between the center of the plurality of quantum wells to a center of the oxide layer may be substantially equal to 0.75 times the emitting wavelength.
The oxide section and the at least one phase matching section may be adjusted such that the 1/e2 width of beam divergence value is between 15-26 degrees.
The oxide section and the at least one phase matching section may be determined such that a corresponding spectral RMS line width value is less than 0.45 nm.
A graded composition layer may be arranged above the oxide layer and a thin layer of Al0.9GaAs may be arranged below the oxide layer.
The oxide layer may be p-doped at 2.5×1018 cm−3.
The light emitting cavity region may include three InxGaAs quantum wells where x=0, or five InxGaAs quantum wells, where x=0.05-0.3 at between 850-1060 nm emission wavelength.
The bottom mirror may include alternating refractive index layers including AlxGaAs where x=0.12 and 0.9-1 for 850 nm emitting wavelength or with x=0 and 1 for 1060 nm emitting wavelength.
These aspects, features, and example embodiments may be used separately and/or applied in various combinations to achieve yet further embodiments of this invention.